This data field appears on devices in the AV devices category. And corresponds to a PK_Device entry in the Device table, corresponding to the port on your tuner card (the ports appear as child devices on your tuner card).

It's meant for pipes management in LinuxMCE to tell LinuxMCE what tuner card a given AV device is attached to, so it can be enabled when you try to view it (for np_TV or other "Live" media types.)